Typically, floating screed pavers are comprised of a self-propelled paving machine having a hopper at its forward end for receiving material from a dump truck which is pushed along the roadbed by the paver. The truck progressively dumps its load of paving material into the hopper.
A conveyor system on the paver transfers the material from the hopper for discharge on the roadbed. Screw augers then spread the material in front of the screed. The screed is commonly connected to the paving machine by pivoting tow or draft arms, which allows the screed to "float" on the paving material. Accordingly, the screed is commonly referred to as a "floating screed".
The screed functions to level, compact, and set the width of the paving material distributed by the augers; ideally leaving the finished road with a uniform and smooth surface. The height of the tow points on each side of the paver and the angle of attack of the screed may be varied to control the thickness and slope of the paving mat.
For many paving activities, the effective paving width of the screed is adequate. However, for other paving activities, there is a desire to widen the effective paving width of the screed. Consequently, "extendable" screed units have been attached to the main screed unit where the paving width varies and/or there are obstacles to be paved around. Moreover, there has further been a need to provide pivotal movement of the extension screed unit in order to form a sloped shoulder or berm at the edge of the road.
Heretofore, prior art paving machines provide for mechanical control over the screed assembly. Such machines require skilled operators for monitoring and adjusting the extension screed, including such parameters as: the width, height and slope of the extension screed. Moreover, an adjustment of one of the parameters effects other parameters, which may require re-adjustment of the other parameters. Accordingly, it is desirable to provide electrohydraulic technology to automatically control the screed adjustment parameters. It is further desirable to provide for microprocessor control to automatically control the paving width, height, and slope to provide for more accurate positioning of the extension screed unit.